Highly refracting optical glass for correction of high diopter values with low density

ABSTRACT

An optical quality glass suitable for use in eyeglass lenses, characterized by having a refractive index nd of at least 1.70; a specific gravity of not more than 3.0 and a thermal coefficient of expansion Alpha X 107 per *C of not more than 100, which contains at least 90 mol % of metal oxide components having a molecular weight of not more than 100, and which consists essentially of at least 90 mol % of SiO2, B2O3, Li2O, Na2O, K2O, MgO, CaO, ZnO, TiO2 and a crystallization stabilizing amount of up to about 10 mol % of at least one member selected from the group consisting of SrO, BaO, ZrO2, Ta2O5 and Nb2O5.

United States Patent Faulstich et al. Aug. 5, 1975 [5 1 HIGHLY REFRACTING OPTICAL GLASS 3,615,770 10/1971 Faulstich et a1. 106/54 x FOR CORRECTION OF HIGH DIOPTER 3,703,389 11/1972 Bromer et a1 1 1 1 106/47 Q VALUES WITH Low DENSITY 3,740,242 6/1973 Faulstich et al. 106/47 Q X [75] Inventors: Marga Faulstich; Volkmar Geiler; FOREIGN PATENTS OR APPLICATIONS Georg Gliemeroth, a" of Mainz; 1,496,556 9/1972 Germany 106/47 Q Lothar Meckel, Ostrich n of 1,941,374 2/1971 Germany 106/47 Q Germany Appl. No.: 420,369

[30] Foreign Application Priority Data Dec. 2, 1972 Germany 2259183 [52] US. Cl. 106/54 [51] Int. Cl. C03c 3/08 [58] Field of Search 106/47 Q, 54

[56] References Cited UNITED STATES PATENTS 3,266,916 8/1966 Bromer et a1. 106/54 3,477,863 11/1969 Bromer et al. 106/54 Primary Examiner-Allen E. Curtis Assistant Examiner-Thomas A. Waltz Attorney, Agent, or FirmMillen, Raptes & White [5 7 ABSTRACT An optical quality glass suitable for use in eyeglass lenses, characterized by having a refractive index n of at least 1.70; a specific gravity of not more than 3.0 and a thermal coefficient of expansion a X 10 per "C of not more than 100, which contains at least 90 mol of metal oxide components having a molecular weight of not more than 100, and which consists essentially of at least 90 mol of SiO B 0 Li O, Na O, K 0, M O, CaO, ZnO, TiO and a crystallization stabilizing amount of up to about 10 mol of at least one member selected from the group consisting of SrO, BaO, ZrO Ta,,O and Nb O 6 Claims, N0 Drawings HIGHLY REFRACTING OPTICAL GLASS FOR CORRECTION OF HIGH DIOPTER VALUES WITH LOW DENSITY BACKGROUND OF THE INVENTION The invention relates to optical glass compositions having a relatively high refractive index of at least 1.70 and a relatively low cgs density or specific gravity (s) of at most 3.0. Highly refracting optical glasses heretofore have been offered on the eyeglass market and used for spectacle glasses with high diopter values, but such glasses have relatively high specific gravities above 3.7, e.g., Schott BaF 50, s 3.8; Schott SF 15, s 4.06 g/cm and the like.

In order to achieve a high refractive index 1 d of 1.70 or higher together with low nu values v, e.g., of 35 or less in optical quality silicate glasses suitable for eyeglass lenses, it has generally been thought necessary to utilize flintor bariumflint-glass compositions containing a high heavy metal-oxides content, e.g., of leadand/or barium,-/and lanthanoxide which has resulted in high densities of 3.7 and higher.

For diopters of -8 to 25, these prior art spectacle glasses require very large rim thicknesses, for diopters +8 require very large center thicknesses and have relatively high weights; this is a great disadvantage from both the aesthetic and practical points of view.

The physical and chemical properties required of optical quality glass for use as eyeglass lenses are well established in the art, For example, such glasses must not only be optically clear and free from imperfections but should exhibit a small thermal expansion coefficient a X 10 per C at 2()-300 C of 85 100; they should be capable of being pressed to facilitate manufacture of lens blanks,. The glass preferably has a sufficiently high content of smaller alkali metals, especially Na, to permit chemical hardening by ion exchange with larger alkali metals in compliance with the FDA test guideline.

Furthermore, the glasses must be chemically inert, non-toxic and free of optical defects.

The new glasses have a high E-modulus of -9,50O kp/mm and, therefore, have a higher strength than the usual, comparable flint glasses the E-modulus of which is -6,10() kp/mm'-.

OBJECTS OF THE INVENTION Accordingly, it is a general object of this invention to provide highly refractive optical quality glass which is substantially lighter in weight than those presently commercially available.

Another object of this invention is to provide highly refractive, lightweight eyeglass lenses.

A further object of this invention is to provide a glass having these properties which can be fused with common optical quality crown glasses so as to form achromatic doublet lenses.

An additional object of this invention is to provide such optical quality glasses which are easily processable into eyeglass lenses.

Upon further study of the specification and appended claims. further objects and advantages of this invention will become apparent to those skilled in the art.

SUMMARY OF THE INVENTION Briefly, the above and other objects are attained in one aspect of the present invention by providing an optical quality glass suitable for use in eyeglass lenses, characterized by having a refractive index 17d of at least 1.70; a specific gravity of not more than 3.0 and a thermal coefficient of expansion 01 X 10 per C of not more than 100, which contains at least 90 mol of metal oxide components having a molecular weight of not more than 100, and which consists essentially of at least 90 mol of SiO B 0 Li O, Na O, K 0, MgO, CaO, ZnO TiO and a crystallization stabilizing amount of up to about 10 mol of at least one member selected from the group consisting of SrO, BaO, ZrO Ta O and Nb O said glass being further characterized by consisting essentially of, in parts by weight per 100 parts of glass:

a. 40-45 wt SiO and 2-6 wt B 0 the total SiO and B 0 being 42-49 wt b. 12-17 wt total Li O, Na O and K 0, including 6-16 wt Na- O; c. 24-26 wt TiO and d. 2-7 wt ZrO DETAILED DISCUSSION The glasses of the present invention, which consist essentially of at least 90 mol of SiO- -B- O -alkali metal oxides-MgO-CaO-ZnO-Ti0 and not more than 10 mol of SrO-BaO-ZrO -AI O -La O -Nb O -Ta O have the following properties:

a. Refractive index 17d 2 1.70, generally 1.70-1.71 b. Specific gravity (cgs) 3.0, generally 2.9-3.0 c. Expansion coefficients a l0 5 100 at 20300C,

generally -100 The glasses according to the invention can d. optionally be fused with a spectacle crown glass of mi 1.523, e.g., vd 58.9 specific gravity (cgs) 2.54 expansion coeff. a X 10 f/O6 at 20-300C 96 transformation temperature T (C) 540 e. are capable of being pressed by conventional techniques;

f. have a high E-modulus, e.g., of 9,400-9,6OO

g. can be chemically hardened, e.g., by ion exchange (the FDA test is met).

The glasses according to the invention consist essentially of SiO -B O -alkali metal oxides-ZrO- -TiO and can be crystallization-stabilized with a crystallization stabilizing amount of up to about 10 mol of at least one member selected from the group consisting of CaO, MgO, SrO, BaO, ZnO, AI O La O Ta O and Nb O The glasses according to the invention comprise at least mol of metal oxides which have a molecular weight not greater than 100.

The glasses advantageously have the following composition, in weight of the total composition:

-Continued Useful Preferred SrO 040% 34'/z* 8110 -1071 0-10% ZnO 0-7% 1 541.5% A1 0. 0-2% 0-17: 1.21 0 0-5% 04% Nb. .o,-, 04% 1471* Ta O 04% 0-371 optional ingredients; prcfcrred range when present.

Up to 5 of BeO and CdO can be introduced for further crystallization stabilization. Both components are, however, generally avoided for use in eyeglass lenses because of their toxicity.

La O can be wholly or partially replaced by an equivalent molar quantity of Y O Similarly, a part, e.g., 0 3 mol of the SiO can be replaced by GeO The cost of the raw materials for both replacement components is presently so high that they are economically not introduced. Nb O can similarly be replaced by up to an equivalent molar quantity of Ta o Again for reasons of economy, thetotal content of Nb O and/or T21 0 should likewise be kept as small as possible.

For refining these glasses, an AS 0 content of 0.3

is generally sufficicnt', however, depending on the method employed in producing the melt, a higher content of A5 0 or other conventional refining agents can be used, e.g., up to 1 7(, as is known in the art.

The glasses have very good chemical stability, i.e., as proved by Chemical Properties tests (Schott Optical Glass, catalogue No. 3060172 d 1X l720o.p.:

a. Resistance to climatic variations KWB class 1 b. Resistivity to Staining Staining class 0 c. Acid resistance Class 1-2 and can be groundand polished in the same way as conventional optical glasses.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative and not limitative of the remainder of the disclosure in any way whatsoever. in the following Examples, the temperatures are set forth uncorrected in degrees celsius; unless otherwise indicated, all parts and percentages are by weight.

Table 1 shows examples for glasses according to the invention in percentages by weight; Table 2 shows them in molar percentages.

TABLE 1 Glass Compositions in wt. 7:

Metal Oxides Example 1 2 3 4 5 6 7 8 9 SiO 43.3 43.3 41.75 43.60 42.00 42.00 41.95 41.0 44.0 B 0 2.75 5.0 2.75 5.00 5.00 3.00 2.75 3.0 3.0 Li O 1.00 2.4 1.00 2.40 4.00 1.00 1.0 Na ,O 10.10 6.0 10.00 6.00 6.00 15.00 14.00 14.0 12.0 K 0 4.75 7.0 6.00 7.00 7.00 1.00 2.0 CaO 2.00 6.0 2.00 6.00 6 00 2.0 6.0 SrO 3.50 4.00 3.00 4.0 BaO 10.00 ZnO 1.50 1.50 6.20 2.0 Al: o 0.3 L320" 4.0 ZrO 3.00 5.0 3.00 5.00 5.00 5.00 4.00 6.0 6.0 Ti0 25.10 25.00 25 .00 25.00 25.00 25.00 25.10 25.0 25.0 Nb o 3.00 3.00 1.00 n 1.709 1.702 1.7042 1.700 1.707 1.702 1.705 1.705 1.7154 v,, 30.0 31.2 30.5 31.5 31.5 30.7 30.2 31.0 30.3 s[g/cm"] 2.95 2.88 2.95 2.85 2.86 3.0 2.98 a 1 10" 94 93 98 92 99 96 87.5

TABLE 2 Glass Compositions in mol 72 Metal Oxides Example 1 2 3 4 5 6 7 8 9 SiO 49.8 47.9 48.5 48.0 45.5 49.8 47.6 46.6 50.5 B 0 2.7 4.8 2.8 4.8 4.7 3.1 2.7 2.9 3.0 Li. ,O 2.3 5.3 2.3 5.3 8.7 2.3 2.3 Na. ,O 11.2 6.4 11.2 6.4 6.3 17.3 15.5 15.4 13.3 K 0 3.5 4.9 4.4 4.9 4.8 0.7 1.4 (a0 2.5 7.1 2.5 7.1 7.0 2.4 7.4 SrO 2.4 2.7 2.0 2.6 BaO 4.6 ZnO 1.3 1.3 5 2 1.7 A1 0;, 0.2 La Q, ZrO 1.7 2.7 1.7 2.7 2.6 2.9 2 2 3.3 3.3 TiO 21.8 20.7 21.8 20.8 1.4 22.3 21.5 21.4 21.7 Nh O 0.8 0.8 0.3 n,, 1.709 1.702 1.7042 1.700 1.707 1.702 1.705' 1.705 1.7154 v,, 30.0 31.2 30.5 31.5 31.5 30.7 30.2 31.0 30.3 s[g/cml 2.95 2.88 2.95 2.85 2.86 3.0 2.98 a 10 94 93 98 92 99 )6 87.5

20-300C Tg (C) 556 535 542 53) 518 586 Further examples of optical glasses similar to those of the tables and within the scope of applicants invention are as follows. in weight 70:

Example 10 Example 11 SiO- 43.0 7! SiO, 41.7. 7r B 2.75% B 0 2.7. /2 L1 0 1.0 '7: L1 0 1.0 7: Na 0 10.0 7: Na O 14.0 7' K 0 4.75% K 0 2.0 '7! CaO 2.0 7! ZnO 3.5 71 S10 3.5 "/1 SrO 4.0 '7 ZnO 1.5 7( TiO 25.0 "/1 210 3.5 7: 2x0: 4.0 7: Ti0 25.0 7: Nbgon 1.0 7: Nb O 0.3 7: A5 0, 0.3 7( A5 0, 0.3 7 h 1.7089 n,, 1.700 v,, 30.1 v,, 30.8 a X 10 94 a X 10 100 -300C 20-300C Tg (C.) 556 Tg(C.) 543 s 2.95 s 2.96

MELTING EXAMPLE FOR 150 KG OF GLASS The raw materials of the following batch are weighed out:

The batch is thoroughly mixed and melted at 1,400 i 20C in about 8 hours. After the melt has become clear, it is refined for 3 hours and stirred for 1 hour to the discharge temperature of 890C. During discharge, the melt is worked into gobs or pressed elements. The batch can also be continuously melted in a trough. The glass has the following physical properties:

1 d 1.7042 ;Vd 30.5 aXl0 /C at (20-300C) 98 Tg (C) 542 S (g/cc) 2.95

The proceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.

What is claimed is: 1. An optical quality glass suitable for use in eyeglass lenses, characterized by having a refractive index 17:! of

atleast 1.70; a specific gravity of not more than 3.0 and a thermal coefficient of expansion a X 10 per C of not more than 100, which contains at least mol of metal oxide components having a molecular weight of not more than 100, and which consists essentially of at least 90 mol of SiO B 0 Li O, Na O, K 0, TiO MgO, CaO, ZnO and a crystallization stabilizing amount of up to about 10 mol of at least one member selected from the group consisting of SrO, BaO, ZrO Ta O and Nb O said glass being further characterized by consisting essentially of, in parts by weight per parts of glass:

a. 40-45 wt SiO and 2-6 wt B 0 the total SiO and B 0 being 42-49 wt b. 12-17 wt total Li O, Na O and K 0, includin 6-16 wt Na O; c. 24-26 wt TiO and d. 2-7 wt ZrO 2. An optical glass according to claim 1, consisting essentially of, in by weight of the total composition:

3. An optical glass according to claim 2, having properties of consisting essentially of, in by weight:

Slo 41 7571 2 c Na O 10.0% K 0 6.07 C 2.07: SrO 4.0% ZnO 1 .57: TiO- 25 .07: ZrO- 3.0% Nh o; 3.07:

and As ,O, 0.3%.

4. An optical glass according to claim 2, having the properties of "a 1.708); V 30.1; 0: X 10 94; 20-300C y (C) 556'. and

. 7 8 which .optical glass Consists essentially of, in by 61 136 weight, T,, (C 543;

density(s. gm/cc) 2.96.

510. 43.0% 2.75% 5 WhlCh consists essentially of, m by weight. Li O 1.0% M 10.0%

K 0 4.75% SiO 41.75% (110 2.0% 13 0. 2.75% SrO 3.5% Li O I 1.0% ZnO 1.5% 0 14.0% zro 3 5% l0 K 0 2.0% Tio 25.0% o 3.5% Nb O 0.3% s o 4.0% and A3 0 0.3%. TiO 25.0% zro 4.0% .5 A b2O.-, 1.0% n optical glass according to claim 2, having the and ASOq 03% properties of 6. The glass composition of claim 1 in the form of an n L700; eyeglass lens. v 30.8; 

1. AN OPTICAL QUALITY GLASS SUITABLE FOR USE IN EYEGLASS LENSES, CHARACTERIZED BY HAVING A REFRACTIVE INDEX ND OF AT LEAST 1.70, A SPECIFIC GRAVITY OF NOT MORE THAN 3.0 AND A THERMAL COEFFICIENT OF EXPANSION AX10**7 PER *C OF NOT MORE THAN 100, WHICH CONTAINS AT LEAST 90 MOL % OF METAL OXIDE COMPONENTS HAVING A MOLECULAR WEIGHT OF NOT MORE THAN 100, AND WHICH CONSISTS ESSENTIALLY OF AT LEAST 90 MOL % OF SIO2, B2O3, LI2O, NA2O, K2O, TIO2, MGO, CAO, ZNO AND CRYSTALLIZATION STABILIZING AMOUNT OF UP TO ABOUT 10 MOL% OF AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF SRO, BAO, ZRO2, TA2O5 AND NB2O5, SAID GLASS BEING FURTHER CHARACTERIZED BY CONSISTING ESSENTIALLY OF, IN PARTS BY WEIGHT PER 100 PARTS OF GLASS, A. 40-45 WT % SIO2 AND 2-6 WT % B2O3, THE TOTAL SIO2 AND B2O3 BEING 42-49 WT %, B. 12-17 WT % TOTAL LI2O, NA2O AND K2O, INCLUDING 6-16 WT % NA2O, C. 24-26 WT % TIO2, AND D. 2-7 WT % ZRO2.
 2. An optical glass according to claim 1, consisting essentially of, in % by weight of the total composition:
 3. An optical glass according to claim 2, having properties of
 4. An optical glass according to claim 2, having the properties of
 5. An optical glass according to claim 2, having the properties of
 6. The glass composition of claim 1 in the form of an eyeglass lens. 